Abstract : In the last few years, new devices such as palm computers, smart phones, pocket PCs became common components of the computing infrastructure. These devices allow multimedia information to be used on the Web at any time and anywhere. At the same time, the content of the Web has known an important revolution. Today, the Web includes continuous medias such as video, audio and 3D animations. The content is created in several formats with new functionalities. Usually, these formats are based on many structural dimensions: logical, spatial, temporal and hypermedia.

In order to ensure universal access to Web content, with respect to the constraints of the current environment, it is necessary to design new systems that enable content delivery in different contexts. The objective of our work is to resolve the problems related to content adaptation and negotiation based on the limitations of the target devices and the heterogeneous environment. We propose a flexible architecture called NAC (Negotiation and Adaptation Core) that includes different components for content negotiation and adaptation, and ensures an efficient framework in which these components cooperate and exchange negotiation-based information in order to reach the objective of the universal access.

NAC allows several kinds of adaptations to be applied: structural adaptation, semantic adaptation and media resources adaptation. These adaptations satisfy different contexts of the clients (terminal capabilities, user preferences, etc.). We also propose a description model of the environment context: UPS (Universal Profiling Schema), a negotiation protocol and a rich collection of adaptation techniques. NAC concepts have contributed in W3C standardization efforts, in particular in the CC/PP framework and in work on Device Independence. This work includes performance evaluations in order to show the usability of our system in a practical framework.